1. Field of the Invention
The invention relates to an adjusting element having a cylinder, the interior space of which contains a medium under pressure, a piston which is displaceably arranged in the cylinder and has a piston rod which projects from the cylinder at one end of the cylinder, and an annular seal which bears tightly with its inner radially encircling circumference against the piston rod and with its outer radially encircling circumference against the inner wall of the cylinder. The pressure of the medium is applied to the seal on its side facing the interior space; its side remote from the interior space is supported on a supporting element which in turn, with its end remote from the annular seal, is supported on part of the cylinder, and having a safety element which is made of a meltable material, as a result of which a passage opening can be produced from the interior space of the cylinder to the environment.
2. Description of the Related Art
In such adjusting elements, which are preferably gas springs, the interior space filled with the medium can be connected to the environment if a certain internal pressure in the cylinder is exceeded in order to avoid a high internal pressure in the cylinder. An excessively high internal pressure, which may occur due to a temperature increase, for example in the event of a fire in the environment of the adjusting element, may result in the cylinder being destroyed or in the piston rod being forced out of the cylinder.
Gas springs of this type can be pneumatic adjusting elements for easy manipulation of the luggage trunk or the hood of a motor vehicle, these adjusting elements forming a counterbalance for the parts adjusted.
U.S. Pat. No. 5,485,987 discloses an adjusting element of the type mentioned at the beginning. If a certain bearing force of the annular seal against the supporting element is exceeded, the annular seal is displaced towards the discharge opening of the piston rod from the cylinder and thus clears a hole in the cylinder, via which the interior space of the cylinder is connected to the environment, so that the medium contained in the cylinder can escape into the environment. In this case, it is a disadvantage that moisture can enter the cylinder through the hole, a factor which leads to corrosion.
U.S. Pat. No. 5,862,893 discloses an adjusting element whose piston rod is centred relative to the cylinder by a piston-rod guide. An annular seal which is secured by the piston-rod guide and a fixing sleeve is provided in order to seal the piston rod. The position of the fixing sleeve is determined by an encircling bead in the cylinder. Provided further downstream of the bead is a second sleeve which is prestressed relative to the inside diameter of the cylinder and is thus held radially and axially in its installed position. The second sleeve forms a stop for the piston and thus limits the outwards movement of piston and piston rod. The second sleeve is made of a material which can melt above a specific temperature. If the temperature increases above the specific temperature, the sleeve melts and the piston together with the piston rod can be displaced further outwards. In the process, a cross-sectional constriction arranged in the piston rod passes into the region of the annular seal, so that a bypass to the environment is created, via which bypass the gas contained in the cylinder can escape. This cross-sectional constriction of the piston rod, necessary in order to form the bypass, leads to weakening of the piston rod. Due to the arrangement of the sleeve made of meltable material, the adjusting device requires a larger axial construction space than conventional adjusting devices.